Fiber Bragg gratings (FBGs) are commonly used in fiber optic systems for measuring physical quantities such as temperature, pressure, and strain at a plurality of sensors. A number of different approaches have been used for the interrogation of FBGs, that is, for determining the center wavelength of the reflection spectrum of each FBG. The prior approaches have several shortcomings, however, that render their usefulness limited for practical applications. Some of these shortcomings include:                Limited number of FBGs that can be interrogated along a single optical fiber;        Instability of optical source output properties;        Wavelength errors due to stable optical source ripple phase;        Susceptibility to intensity and spectrum changes in components that can cause wavelength errors;        Susceptibility to power supply noise;        Wavelength errors due to low frequency receiver output drift;        Errors due to multi-FBG source spectrum masking; and        Wavelength uncertainty due to low signal-to-noise resulting from very short analog-to-digital conversion times.Therefore, there remains a need to mitigate the above-mentioned problems.        